Prox1 mRNA expression in the medial cortex of the turtle (Pseudemys scripta elegans).

The medial cortex of the cerebrum in reptiles is thought to be homologous to the mammalian dentate gyrus, based on cytoarchitectures, fiber connections, and neurochemical profiles. To support this hypothesis, we examined the mRNA expression of vesicular glutamate transporter 1 (vGluT1), a glutamatergic gene marker, and Prox1, a selective gene marker for granule cells of the dentate gyrus, in the turtle medial cortex (zone 2). Reverse transcription-polymerase chain reaction revealed the presence of both mRNAs in the turtle cerebrum. In situ hybridization of zone 2, which is a layer of densely packed neurons in Nissl stains, intensely expressed vGluT1 and Prox1. In zone 3, which is a loosely packed layer, vGluT1 was intensely expressed, whereas Prox1 signals gradated from strong to negative toward zone 4. These findings demonstrate that zone 2 contains glutamatergic neurons and expresses Prox1 mRNA and suggest that zone 2 in the turtle cerebrum is homologous to the mammalian dentate gyrus.